The influence of hydrodynamics on the behaviour of European Eel at anthropogenic structures

Collier, Stephen

Abstract

Highly fragmented river networks in the UK pose a serious threat to the viability of anadromous fish, including the critically endangered European eel (Anguilla anguilla), thus necessitating remediation at anthropogenic riverine obstructions to restore connectivity. The current causes of the decline of the European eel, fish behavioural cues, and current management measures were reviewed to assess gaps in current understanding of European eel passage and identify key areas of research to improve prospects for the species. This thesis identified eel responses to hydraulic fields at obstructions and experience of impingement as key gaps in understanding. These gaps were addressed through the following objectives: 1, quantifying 3D flow-fields through combined numerical modelling and field measurements; 2, recording eel movements in regions of variable hydraulics in controlled field and laboratory experiments; and 3, by contextualising recorded eel movements with modelled flow-fields.
Eel movements captured with sonar imagery approaching pumping stations or infrared cameras within a laboratory flume were contextualised in three-dimensional models allowing the exploration of specific hydraulic conditions eels experienced. Numerical models were validated using acoustic doppler velocimetry taken in both laboratory and in the field. Behavioural analysis focused on previously observed response hydrotaxis: considering the magnitudes and rates of changes in hydraulic variables that individual eels experienced to improve understanding of fish decision making in regions of complex flow.
Observed eel behaviour demonstrated that individuality was an important factor in the distribution of response locations when approaching structures. Juvenile eels approaching wedge-wire screens exhibited tactile responses resulting from very small regions of rapid hydraulic change that did not allow sufficient time or space for behavioural response prior to screen contact. Local flow conditions at screens remained important for impingement, which varied considerably for different screen apertures and bulk flows and thus an eel’s ability to escape the screen. Adult eel movements at field sites showed variable responses to similar hydrodynamic conditions: magnitudes of change in velocity magnitude, strain rate, dynamic pressure and vorticity that influenced some eel behaviour was ignored by others, emphasising that individuality was an important factor in fish decision-making. Responses predominantly took place in regions of changing hydrodynamics and was indicative that eels investigated accelerating flow to aid in downstream passage until they identified conditions as hazardous. This not only demonstrated the potential efficacy of the bypass in attracting outbound adult eels, but also underlined that flow conditions downstream of other structures also influence fish passage behaviour.

Citation

Collier, S. (2025). The influence of hydrodynamics on the behaviour of European Eel at anthropogenic structures. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/5086316

• Thesis Type: Thesis
• Deposit Date: Mar 20, 2025
• Publicly Available Date: Jan 8, 2030
• Keywords: Biological science ; Environment
• Public URL: https://hull-repository.worktribe.com/output/5086316
• Additional Information: Biological Sciences; Energy & Environment Institute; University of Hull
• Award Date: Jan 7, 2025